Recently, in accordance with an increase in cost of an energy source due to exhaustion of fossil fuel and interest in environmental contamination, the demand for an eco-friendly alternative energy source has become an essential factor for future life. Therefore, research into various power generation technologies such as a nuclear power generation technology, a photovoltaic power generation technology, a wind power generation technology, a tidal power generation technology, and the like, has been continuously conducted, a power storage device for efficiently using energy produced as described above has also been interested.
Particularly, as the development of a technology and the demand for a mobile device have increased, the demand for a battery as an energy source has rapidly increased, and thus, various research into batteries capable of satisfying various requirements has been conducted.
Representatively, in view of a shape of the battery, a prismatic secondary battery and a pouch type secondary battery capable of being applied to a product such as a mobile phone, or the like, due to a thin thickness are in high demand, and in view of a material, lithium secondary batteries having advantages such as high energy density, a discharge voltage, output stability, for example, a lithium ion battery, a lithium ion polymer battery, and the like, are in high demand.
In addition, the secondary battery is classified depending on a structure of an electrode assembly in which a cathode, an anode, a separator interposed between the cathode and the anode are stacked. A representative example of the electrode assembly includes a jelly-roll type (winding type) electrode assembly having a structure in which long sheet-type cathodes and anodes are wound in a state in which a separator is interposed therebetween, a stacking type (laminate type) electrode assembly in which a plurality of cathodes and anodes cut at a predetermined size are sequentially stacked in a state in which a separator is interposed therebetween, and the like. Recently, in order to solve problems of the jell-roll type electrode assembly and the stacking type electrode assembly, as a more improved electrode assembly corresponding to a mixed form of the jelly-roll type electrode assembly and the stacking type electrode assembly, a stack/folding type electrode assembly having a structure in which unit cells obtained by stacking predetermined unit cathodes and anodes in a state in which a separator is interposed therebetween are sequentially wound in a state in which these unit cells are positioned on a separation film has been developed.
Further, depending on a shape of battery case, the secondary battery is classified into cylindrical and prismatic batteries in which electrode assemblies are embedded in cylindrical or prismatic metal cans, respectively, and a pouch type battery in which an electrode assembly is embedded in a pouch type case made of an aluminum laminate sheet.
In particular, recently, a pouch type battery having a structure in which a stacking type or stack/folding type electrode assembly is embedded in a pouch type battery case made of an aluminum laminate sheet has received much attention due to low manufacturing cost, a light weight, and ease of changing a shape, and the like, and a use amount of this pouch type battery has gradually increased.
FIG. 1 is a mimetic view schematically illustrating a structure of a pouch type battery cell according to the related art.
Referring to FIG. 1, a battery cell 100 has a structure in which outer peripheries 112 of a pouch type battery case 110 made of a laminate sheet are sealed by thermal bonding in a state in which an electrode assembly 120 is accommodated in an accommodation part 111 of the battery case 110.
The electrode assembly 120 includes cathode and anode tabs 121 and 122 protruding toward both outer peripheries opposing each other, wherein the cathode and anode tabs 121 and 122 are connected to cathode and anode leads 131 and 132, respectively, and the cathode and anode leads 131 and 132 protrude outwardly of the battery case 110 in a state in which the cathode and anode leads 131 and 132 are connected to the cathode and anode tabs 121 and 122, respectively.
The cathode and anode taps 121 and 122 have the same size as each other, and the cathode and anode leads 131 and 132 have the same size as each other.
One of main research projects in the battery cell as described above is to improve safety. For example, explosion of the battery may occur due to a high temperature and a high voltage in the battery which may be caused by an abnormal operation state of the battery cell, for example, an internal short-circuit of the battery cell, an overcharge state of the battery cell in which a current and voltage exceed an allowable current and voltage, exposure of the battery cell to a high temperature, deformation of the battery cell by dropping or external impacts, and the like.
Particularly, as one of the safety problems, when the internal short-circuit occurs in the battery cell due to exposure to a high temperature environment, malfunction, or the like, a decomposition reaction occurs in a cathode interface, and thus, a large amount of gas is generated. As a result, the battery case is ruptured due to an increase in internal pressure, such that the gas is discharged to the outside of the battery cell.
Generally, this internal gas includes components toxic to human bodies such as carbon monoxide, and the like, thereby causing a safety problem.
Therefore, a technology capable of basically solving this problem has been urgently required.